If you want to tank effectively you'll want to pick circle of the moon for better shapeshifting. If you go this route don't forget a druid is still a full caster with access to level 9 spell slots. And like pallys and clerics you have access to your full spell list, with the ability to swap spells at the end of a long rest.
You can be a huge meat shield and still use a variety of spells. Narrowing your role as a druid is difficult because the class was designed around versatility. Choosing your circle and feats will help define your role at least a little.
Finally an important aspect of druids is planning. After each long rest think about the challenges the party might face and choose your spells accordingly.